This invention relates generally to display devices and particularly to a data line defect avoidance structure for display devices, for example liquid crystal displays.
Liquid crystal television and computer displays are known in the art. A simplified prior art liquid crystal display is shown in FIG. 1. The display includes an array of liquid crystal display elements 11 arranged in rows and columns. Each display element is associated with a switching device 12, such as a thin film transistor (TFT). The gate of each TFT 12 is connected to a select line 13 whereby a complete row of TFT's is simultaneously biased on by each select line 13. The select lines 13 are electrically connected to the output terminals 17 of a select line scanner 21, which provides the biasing voltages to the select lines. Data lines 14-1 through 14-N extend between the columns of display elements 11. The display elements 11 are connected to the data lines 14 by the conduction paths of the TFT's 12. The individual data lines 14 are connected to output terminals 15 of it data line scanner 16. The data lines 14 individually apply brightness voltages to the respective columns of display elements.
Liquid crystal displays for television and computer monitors have a large number of columns of display elements, for example 1,440. A data line 14 and a data line scanner stage are needed for every column of display elements. Accordingly, 1,440 data lines, and 1,440 data line scanner stages are required for the display. Each line is only microns wide and every scanner stage includes a number of solid state devices. For these reasons, the probability that one, or more, scanner stages includes a defective solid state device, or that one, or more, data lines includes an open circuit is very high. A faulty scanner stage is a serious defect because the result is a permanent visible line extending the full length of a column. An open in a data line, such as 18 shown in FIG. 1, is also a serious defect. Display elements which are located on the data line scanner 16 side of an open will receive the proper brightness voltages and operate in the normal fashion. However, display elements which are located on the other side of an open will not receive brightness voltages and therefore these display elements will appear as a permanent visible line in the display. Such visible lines are unacceptable for television and computer monitor uses.
The open data line problem has been addressed in tile prior art by providing a single repair line 19 immediately outside of the display area. Repair line 19 passes over, but is insulated from, the ends of data lines 14-1 through 14-N. The permanent visible line result of an open 18 is avoided by using repair line 19 to connect the open data line to a fully conductive unopen data line. For example, data line 14-3, which includes open 18, and either unbroken data line 14-2 or 14-1 can be welded to repair line 19, preferably using laser welding. Connecting non-adjacent data lines can be preferable because it prevents adjacent data lines from getting the same brightness signal, thereby resulting in a less noticeable defect. Also, repair line 19 is opened on both sides of the two data lines which have been connected together. The opening of repair line 19 is needed to isolate the connected data lines from the remainder of repair line 19 in order to make the remainder of the repair line available for use with other open data lines. The opening of repair line 19 also decreases the parasitic capacitance of the repair line. After the welding and cutting are complete, the display elements which are located on the data line scanner side of defect 18 continue to receive the proper brightness voltages. The display elements which are located on the other side of defect 18 will receive the same brightness voltages as the data line to which they have been connected, data line 14-2 in the example given. Such display elements are thus turned on and off along with the other display elements in the selected row, although they receive the wrong brightness voltages. However, the improper brightness of a portion of one column is a much less noticeable defect than a permanently visible line. The prior art technique is disadvantageous because the avoidance of every data line defect 18 requires two welding and two cutting steps and therefore is time consuming and costly. The prior art technique is also disadvantageous because the effects of defective data line scanner stages can not be avoided using the technique. For this reason there is a need for a data line defect avoidance structure which substantially decreases the number of repair steps needed to avoid the adverse effects of an open data line and which permits the avoidance of the adverse effects of failed data line scanner stages. The present invention fulfills these needs.